I "feed" a pair of 3880s and P800 printers. Mostly, I buy out of date inks on eBay and as long as they are within about ten years, and if the price it right, I'll make a buy.
I think the main problem from what I understand is that if the ink just sits on a shelf for years without any movement, the pigments may settle.
All four of my printers are second-hand purchases, and two have been overhauled. Mostly the ink that came with them was from a couple years beyond the "expiration" and some many more years.
I also have an Epson 9900 large format printer that keeps printing away and most the inks go out of date before I use them up and replace them with out of date inks.
I've made prints with fresh inks and when I compare them with the same printer but OOD inks made later, I can't see any difference.
I think the trick is if you use older inks, make sure you give them a good shake and if you have older inks in your printer, make it a point every few months to pop out the carts and give them a shake.
There may be issues I'm not aware about using older inks, but in years of experience, I haven't experienced any problems with my printers nor have I seen any issues with my prints. The only problem I have occasionally is that I need to run a nozzle check and a cleaning cycle or two to get a good test pattern.
Once I get that good pattern, the printers are dialed in and keep on going and going.
As always, YRMV. Maybe I've been lucky over the years and the ink was kept out of the heat and that could affect its quality, but I'll keep rolling the dice...
Bottom line is that if the head is spitting out ink properly and the prints looks good, simply keep using the old ink until you need to replace the cartridge.
Oh, and BTW, I've never used any third-party inks and that may be another reason my collection of printers seldom give me grief and keep printing and printing just fine.
